To get a full understanding of the function and metabolism of vitamin A much further knowledge is required. The proposed study aims at elucidating some of the basic characteristics of the vitamin A metabolism, especially as regards the role of the vitamin A-binding proteins. Thus, the amino acid sequences of rabbit and rat RBP will be completed and compared to the amino acid sequence of piscine pRBP, which also will be analyzed. The sequence analyses will be complemented by the elucidation of the three-dimensional structure of human RBP. These analyses, which will be performed by X-ray crystallography, will also reveal pRBP binds retinol. The amino acid sequence of rat liver cRBP will be completed and the homologous myelin protein P2 will be examined as to its possible content of a retinoid derivative. The retinoic acid binding protein, cRABP, will also be sequenced and its relationship to pRBP and cRBP will be examined. The possibility that pRBP and cRBP are regulatorily phosphorylated will be explored. The biosynthesis of pRBP and prealbumin will be examined in hepatocytes derived from normal and vitamin A-deficient rats. In addition, cell free system will be developed containing enriched mRNA for the two proteins, microsomes and golgi complex. The regulation by retinol of the transfer of pRBP from the endoplasmic reticulum to golgi will be elucidated. Attempts to purify the pRBP plasma membrane receptor will be conducted. With use of lipid vesicles we will try to establish an in vitro system which allows retinol to be taken up by the receptor. The role of vitamin A on the differentiation of keratinocytes in the epidermis and on the differentiation of teratocarcinoma cells will be examined. Particular reference will be given to the subcellular distribution of cRBP and cRAB in differentiating cells. The role of the lens of the eye in catabolizing pRBP will be examined and the distribution and function of Ia-bearing cells of the cornea in vitamin A-deficiency will be elucidated.